This invention relates to an aperture structure for a charged particle beam exposure apparatus, capable of forming a shaped beam of high-accuracy shape and size.
In apertures for charged beam exposure apparatuses, as is generally known, an electrically conductive sheet having a small square opening is set on the optical axis of the optical system of the charged beam exposure apparatus, whereby part of a charged beam emitted from a charged particle source is intercepted as the beam passes through the square opening so that a square image of the beam is formed.
In a conventional aperture for a charged beam exposure apparatus, such as the one disclosed in U.S. Pat. No. 4,263,514, four sheets each having a knife edge on one side are combined so that their respective knife edges intersect at right angles to one another to define a square aperture. In this example, the corners of the square aperture have no roundness. This aperture, however, is subject to the following drawbacks. In order to form a high-orthogonality square opening by combining four sheets, it is essential that the sheets not be dislocated during assembly work. However, the sheets are prone to dislocation as they are adhered to one another. Moreover, the knife edges, which are formed by grinding, are prone to errors in linearity. Thus, it is hard to obtain high-accuracy square apertures. When using such a conventional aperture structure in a charged beam exposure apparatus which can provide charged beams of various shapes, it is necessary to select one or two corners of relatively high orthogonality.